Fatigue Flashcards
Def: Fatigue
a decrease in force or power generating capacity
How does fatigue affect isometric contractions
-reduced force
-reduced rate of force development
-reduced rate of force relaxation
How does fatigue affect concentric contractions
-reduced force
-reduced velocity
(reduced power)
How does fatigue affect eccentric contractions
-reduced force
-reduced velocity
(reduced power)
Why is there not a linear relationship between endurance and % ISO MVC
with greater % ISO MAX, there is a greater effect of occlusion causing a greater decrease in endurance
Compare how fatigue is observed in a MVC vs a submaximal contraction
MVC: start at peak force then decline in force due to fatigue almost immediately observed until complete drop at failure
SUBMAXIMAL: maintain consistent submax force until decline in force that you are able to produce due to fatigue meets force of submax then failure occurs
What is the effect of fatigue on the force velocity relationship
There will be a decline in the ISOmax due to a decreased number of active CB and a decline in Vmax due to a decrease in the rate of CB cycling
Peripheral regions that can be affected during fatigue
Motoneurons, Neuromuscular junction, muscle fibers, Cross-bridge
Cause and pathway of central fatigue
CAUSE:
-failure of volition/ lack of drive
-decreased neurotransmitter concentration
-increased metabolites
-hypoglycemia
-decreased membrane excitability
PATHWAY:
MU drop out = decreased activated fibers = active CB = less force capacity
AND
decrease FR= less summation = decreased activated CB = less force capacity
Cause of motoneuron fatigue
-decreased excitability of motoneurons
-reflex inhibition from metabolites
Neuromuscular junction fatigue
-Ach depletion
-reduced endplate excitability
factors causing excitation-contraction coupling failure
-fuel depletion
-accumulation of metabolites
How does fuel depletion cause fatigue
DECREASE IN ATP
-decreased sensitivity of Ca2+ channels leading to a decrease in the amount of Ca2+ released through the SR resulting in an overall decrease in CB activity
DECREASE IN GLYCOGEN
-decreased sensitivity of Ca2+ channels leading to a decrease in the amount of Ca2+ released through the SR resulting in an overall decrease in CB activity
How does the accumulation of metabolites cause fatigue
ACCUMULATION OF Pi
-decreased sensitivity of Ca2+ channels leading to a decrease in the amount of Ca2+ released through the SR resulting in an overall decrease in CB activity
ACCUMULATION OF H+ ION
-interference with Ca2+ binding troponin leading to a decrease in CB activation
-Decrease in pH may also inhibit release of Ca2+
Factors causing fatigue directly to the CB
DECREASED # OF ACTIVE CB
-decreased ATP prevents full capacity CB cycling
FORCE PER CB
-increased Pi causes a decrease in bond strength and increases the likelihood of detachment
-increased Pi cause a decrease in Ca+/troponin interaction causing an increased requirement of Ca2+
SLOWER ADP RELEASE DURING CB CYCLING
-increased H+ ion may cause slower release
In high intensity isometric training, what factors are going to contribute to fatigue
limited O2
decrease in ATP
decrease in PCr
increases in Pi
increase in H+ ion
In high intensity exercise lasting 4-5 minutes, what factors are going to contribute to fatigue
limited O2
decreased ATP
decreased PCr
increased Pi
increased H+
decrease in glycogen will contribute to an extent
In low intensity exercise lasting around 2 hours, what factors are likely to contribute to fatigue
decrease in glycogen
decrease in hypoglycemia
decreased hydration
increased hyperthermia
limited O2
In HITT exercise, what factors are likely to contribute to fatigue
-fatigue in 1min due to:
decreased ATP
decreased PCr
increased Pi
mainly increased H+ ion
-Glycogen decreases across bouts but not a main contributor to fatigue
How does the rate of force development change with fatigue and why
RFD decreases
-type IIx MU dropout (decrease in MU firing rate)
-decrease rate of Ca2+ release and sensitivity
-decreased rate of CB cycling
How does rate of force relaxation change with fatigue and why does this occur
ROR decreases with fatigue
-slower rate of Ca2+ reuptake
-decreases Ca2+ ATPase activity: SERCA pump
How does fatigue increase risk of injury?
decreased rate of muscle relaxation causes forced stretching ultimately increasing risk for injury
What are the short term focuses during recovery for fatigue
recovering PCr and removing H+/Pi
What are the long term focuses during recovery for fatigue
resynthesizing muscle and liver glycogen
Which aspect of fatigue takes the longest to recover
H+ ions take the longest to decrease in concentration from fatigue
What aspect of fatigue recovers the fastest
ATP followed by PCr and Pi
Describe the idea of complete vs incomplete recovery
COMPLETE RECOVERY occurs when all energy sources and metabolites have returned to resting concentration
INCOMPLETE RECOVERY occurs when all energy sources and metabolites have returned to resting concentration except for H+ ions which take longer to recover
How does PCr recover after fatigue
How does H+ ion recover after fatigue
If a muscle has a greater portion of type II fibers compared to type I what characteristics will this fiber exhibit
- increased initial force
- faster use of glycogen
- faster fatigue
- greater reduction in force with fatigue
- slower recovery of PCr
Def: absolute endurance
time to failure at a given intensity
-set weight/power/speed
Def: relative endurance
time to failure at a relative intensity
-%MVC, % of 1RM, %VO2max
Sex differences in absolute endurance
males have greater absolute endurance
-increased strength at a given load means fewer type of type II and less occlusion
More pronounced advantage in upper body
Sex differences in relative endurance
Females have greater relative endurance, especially at low intensities
-smaller fiber diameter
-smaller II/I ratio
-greater capillary density
-more fat metabolism (glycogen sparing)
-more elastic tissue (SSC) could play a role
How does endurance training affect fatigue resistance
- causes an increase in cardiac output, leading to an increased VO2max, resulting in increased absolute and relative endurance
-increased muscle oxidative capacity
increased mitochondrial density
increased myoglobin
increased capillarization
ATP in type I fibers
A) does not experience a large reduction in concentration
B) Is used to replete PCr during recovery
C) Is used to produce CB cycling during exercise
D) all of the above
D
WHERE DO FEMALES HAVE THE GREATEST ADVANTAGE IN ENDURANCE?
A) relative endurance at low exercise intensities
B) relative endurance at high exercise intensities
C) absolute endurance at low exercise intensities
D) absolute endurance at high exercise intensities
A
Dom and Adrienne are both squatting 100Kg
-Dom does 12 reps to failure
-Adrienne does 13 reps to failure
DOSE THIS MEASURE ABSOLUTE OR RELATIVE ENDURANCE?
WHO HAS THE HIGHER ____ ENDURANCE?
Absolute endurance
Adrienne’s is higher
Anjali 1RM squat 100kg
Angelique 1RM squat 150kg
-Anjali can do 15 reps of 50kg before failure and 5 reps of 75kg before failure
-Angelique can do 30 reps of 50kg before failure, and 10 reps of 75kg before failure
WHO HAS GREATER ABSOLUTE ENDURANCE?
WHO HAS GREATER RELATIVE ENDURANCE?
Angelique has greater absolute endurance
Anjali has greater relative endurance
The competition demands a running of exactly 14km/h
-Anjali can run for 12 minutes
-Drazen can run of 10 minutes
IS THIS A TEST OF ABSOLUTE OR RELATIVE ENDURANCE?
Absolute endurance
What mechanisms does a decrease in ATP affect during fatigue
Excitation-Contraction Coupling: Decreases sensitivity of Ca channels leading to a reduced release of CA and in turn reduced number of CBs
Direct Effect on CB: decrease the number of active cross-bridges because ATP is required in CB cycling
What mechanisms does a decrease in glycogen affect during fatigue
Excitation-Contraction Coupling: Decreases sensitivity of Ca channels leading to a reduced release of CA and in turn reduced number of CBs
-Also decreases ability to produce ATP
What mechanisms does an increase in inorganic phosphate affect during fatigue
EXCITATION-CONTRACTION COUPLING: Decreases sensitivity of Ca channels leading to a reduced release of CA and in turn reduced Ca troponin interaction
DIRECT EFFECT ON CB: decreases bond strength, increases likelihood of CB disattachment
What mechanism does an increase in H ion affect during fatigue
EXCITATION-CONTRACTION COUPLING: causes interference of Ca binding to troponin and in turn decreases the rate of CB activation
-may inhibit Ca release, or slow ADP release during CB cycling
What factors cause neuromuscular junction fatigue
AcH depletion and reduced endplate excitability
What fatigue factors affect both central and peripheral fatigue
decreased neurotransmitters, increased metabolites, reduced endplate excitability
